CN1247360C - solder paste - Google Patents

Abstract

A solder paste comprising Sn-based lead-free solder powder mixed with a rosin-based flux, wherein the rosin-based flux comprises 0.01-10.0% by weight of at least one salicylamide compound selected from salicylamide and its derivatives, which prevents the formation of solder balls and voids during soft soldering and exhibits good solderability.

Description

solder paste

technical field

The present invention relates to solder pastes for soldering electronic devices, and in particular to Sn-based, lead-free solder pastes.

Background technique

Sn-Pb alloys have been continuously used as solders since ancient times. They have the advantage of low melting point and good welding ability. For example, the most popular, eutectic Sn63%-Pb37% solder has a melting point of 183°C.

Eutectic Sn-Pb solders are also commonly used for soldering electronic devices. Recently, surface mount technology (SMT) has been increasingly used to mount electronic components on printed circuit boards due to SMT's ability to reduce size, increase packaging density and performance, and reduce operating costs. In SMT, soldering is typically performed by a reflow soldering method using a solder paste (also called paste solder) comprising solder powder uniformly mixed with a soldering flux, especially a rosin-based flux. Generally, the reflow soldering method involves feeding solder paste onto a printed circuit board by printing or dispensing (discharging through a dispenser), temporarily fixing chip-type electronic parts on the solder paste by using the adhesion of the solder paste, and A printed circuit board with electronic components on it is heated in a furnace so that the solder melts, securing the components and electrically connecting them to the printed circuit board.

Printed circuit boards removed from discarded electronic devices by dismantling are often disposed of by grinding in shredders and burying in the ground. When rainwater (ie, acid rain), which has been acidified in recent years, contacts powder printed circuit boards buried underground, lead (Pb) in the Sn-Pb solder is precipitated and pollutes groundwater. If a person or animal continues to drink water containing lead for many years, lead builds up in the body leading to lead poisoning. Therefore, it has been recommended in the art to use lead-free solders, which are completely free of lead, during soldering of electronic devices.

Lead-free solder should consist of elements that are not harmful to humans. For example, Cd cannot be used even though it lowers the melting temperature. Currently promising lead-free solders are Sn-based alloys that contain a large proportion of Sn and one or more alloying elements such as Ag, Cu, Bi, In, Sb or Zn.

Among them, Sn-based solders containing Ag (hereinafter referred to as Sn-Ag-based solders) such as Sn-Ag alloys and Sn-Ag-Cu alloys have advantages of easy handling due to their relatively good wettability as lead-free solders. advantage. However, the Sn-Ag-based lead-free solder has a melting point of about 220°C, which is about 30-40°C higher than that of the eutectic Sn-Pb alloy, so the working temperature (heating temperature at the time of soldering) also becomes corresponding higher. Therefore, they may not be suitable for soldering certain heat-sensitive electronic components.

From the standpoint of safety and economy, Sn-based solder containing Zn (hereinafter referred to as Sn-Zn-based solder) is advantageous because Zn is not only a harmless and indispensable element to the human body, but also found to exist in large amounts in Underground, so its cost is lower than Ag, Cu, Bi, In etc. A typical alloy composition for Sn-Zn lead-free solder is Sn-9Zn. This solder has a melting point of 199°C, which is about 20°C lower than that of Sn-Ag lead-free solder, so it also has the advantage of being useful for soldering heat-sensitive electronic parts, which Sn-Ag-based lead-free solder cannot be applied to on the heat-sensitive electronic components.

Compared with the conventional solder paste prepared from Sn-Pb solder powder and the same rosin-based flux, the absence of lead-free solder in the powder containing Sn-based solder (including Sn-Ag and Sn-Zn-based solder) During the mixing of lead solder paste (this type of solder paste is hereinafter referred to as "Sn-based lead-free solder paste") and rosin-based flux, due to the high content of active Sn metal in the solder powder, the solder powder and flux The reaction between the components, especially with the activators usually present in rosin-based fluxes, can easily occur. This reaction may cause a change in the viscosity of the solder paste, and create a problem that the solder paste cannot be fed satisfactorily by printing or spreading.

As a countermeasure, a method may be used, especially in Sn-Ag solder-based solder pastes, in which the viscosity is controlled by reducing the amount of activators such as amine hydrohalides and organic acids added to the rosin-based flux Change, thereby suppressing the reaction of flux and solder powder. However, since this method weakens the activity of the flux, it may lead to the formation of solder balls and adversely affect the wettability of the solder. Therefore, there is a need to control the viscosity variation of Sn-based lead-free solder paste without reducing the amount of activator in the flux.

In addition to the problems described above, solder pastes containing Sn-Zn-based lead-free solder powder (hereinafter denoted as "Sn-Zn-based solder paste") have another problem. Zn is a metal that is prone to oxidation due to its high ionization tendency. Therefore, an oxide layer is formed on the surface of the solder powder in contact with the air, which reduces the wettability of the solder powder. In particular, in the Sn-Zn-based solder paste prepared by using a rosin-based flux, the surface oxidation of the solder powder generated by the reaction with the flux becomes even more serious, so that soldering defects including due to extremely poor solder The wettability of the lead leads to the formation of voids and the formation of solder balls.

In order to increase the wettability of the solder in Sn—Zn based solder pastes, it is conceivable to use rosin based fluxes with increased amounts of activators. However, as described above, the activator tends to react with the solder powder prior to fluxing, and increasing the amount of the activator can rapidly increase the viscosity of the solder paste and interfere with feeding of the solder paste by printing or dispensing.

In Sn-Zn-based solder paste, a method can be used, which is to coat the surface of Sn-Zn-based solder powder with a suitable substance before mixing with the flux to prevent the solder powder from reacting with the flux and causing the surface oxidation. As the coating substance, a rare metal such as Au or Pd, an inorganic oxide formed from a hydrolyzable organosilicon compound or the like, or an organic substance such as imidazole or triazole can be used.

However, such encapsulation increases the manufacturing cost of the solder paste. Also, some types and methods of coating can promote oxidation of the solder powder during the coating operation, and methods are not necessarily effective in improving solder wettability or solderability.

Contents of the invention

The technical problem to be solved by the present invention is to provide a Sn-based lead-free solder paste with improved solderability, minimal viscosity change and good wettability, which can be satisfactorily used in reflow soldering methods.

An object of the present invention is to improve the solderability of a Sn-based lead-free solder paste comprising Sn-based lead-free solder powder mixed with a rosin-based flux, particularly a solder paste comprising an activator.

Another object of the present invention is to provide such Sn-based lead-free solder paste which shows minimal viscosity change and has good wettability.

Another object of the present invention is to provide a Sn-based lead-free solder paste, especially a Sn-Zn-based solder paste, which has good solder wettability and solderability, wherein it can prevent interference with conventional Sn-Zn-based solder The paste effectively meets the surface oxidation of the solder powder without coating the solder powder.

In one aspect, the present invention provides a lead-free solder powder comprising Sn mixed with a rosin-based flux, wherein the rosin-based flux comprises 0.5-10.0% by weight of at least one isocyanuric compound, It is selected from isocyanuric acid and its derivatives which do not have a hydroxyl group.

In another aspect, the present invention provides a lead-free solder powder comprising Sn mixed with a rosin-based flux, wherein the rosin-based flux comprises 0.01-10.0% by weight of at least one salicylamide compound selected from water Salicylamide and its derivatives.

The present invention provides a Sn-based lead-free solder paste that has improved solderability and can be satisfactorily used in conventional reflow soldering methods. As a result, in certain cases, such as solder pastes containing Sn-Zn-based lead-free solder powders that are highly sensitive to oxidation, the use of an activator containing an appropriate amount as usual can provide a solder paste in which the formation of solder balls is inhibited, and it has excellent wetting properties. It is also possible to suppress the viscosity change of the Sn-based lead-free solder paste containing the Sn-based solder powder, including the Sn-Ag-based solder and the Sn-Zn-based solder, thereby making it possible to remarkably prolong the use of this solder. A lead-free solder paste that is easy to print or dispense.

Detailed ways

Rosin-based fluxes commonly used in solder pastes are prepared by dissolving rosin and one or more additives such as activators and thixotropic agents in a solvent. In particular, the type and amount of activator has a great influence on the solder wettability of the solder paste.

Generally, Sn-based lead-free solders have poor solder wettability compared to Sn-Pb solders. For example, compared to the diffusion coefficient of Sn-Pb solder, Sn-Ag lead-free solder diffusion is only equivalent to about 80% of Sn-Pb solder. Sn-Zn lead-free solder has an even worse diffusion coefficient, it diffuses only about 70% of that of Sn-Pb solder.

Therefore, it seems favorable for Sn-based Pb-free solder pastes to incorporate a large amount of activators to improve wettability. However, as mentioned earlier, this results in a rapid increase in the viscosity of the solder paste due to the reaction between the activator and the solder powder. As a result, solder paste quickly becomes difficult to print or feed through a dispenser, and its shelf life or usable life becomes extremely short. Therefore, unless the solder powder is protected by surface coating, the amount of activator should be reduced, resulting in poor wetting. In particular, conventional Sn-Zn based lead-free solder pastes have very poor wettability.

In the reflow soldering process using solder paste, soldering is performed in a heated furnace called a reflow furnace. Heating in a reflow furnace is usually a two-step heating, where first preheating is performed at a temperature of 150-170°C for 30-100 seconds, and then main heating is performed at a temperature 20-50°C above the melting temperature of the solder. Preheating is performed in order to evaporate the solvent in the solder paste and at the same time to reduce thermal shock to the electronic parts to be soldered.

The substances used in solder pastes, still the most popular eutectic Sn-Pb solders, are designed to exhibit optimum performance during this two-step heating. For example, the activator starts to partially react at about 150°C, which is the preheating temperature, and completely reacts at about 210-230°C, which is the main reaction temperature of Sn-Pb solder. In the solder paste of Sn-Pb solder, even if the activators used are active at temperatures as low as 150°C, due to the low reactivity of Pb, no significant oxidation of the solder powder occurs during the preheating stage.

On the contrary, it was found that, with respect to the Sn-Zn-based lead-free solder paste, even in the preheating stage, the zinc exposed on the surface of the Sn-Zn-based solder powder can easily combine with the oxygen in the reflow furnace to form a relatively thick surface oxide layer. If the solder powder having such an oxide layer formed by oxidation during preheating is mainly heated, the solder powder melts together with the oxide layer covering its surface, so it remains like a solder ball without spreading. In addition, by reacting with the surface oxide layer on the solder powder, the flux is mostly consumed and loses its activity, leading to poor wettability and to the formation of voids inside the solder joints obtained. The formation of these solder balls and voids leads to the formation of solder defects.

As already stated, lead-free solders based on Sn—Zn are highly sensitive to surface oxidation due to Zn's high ionization tendency and susceptibility to oxidation. In particular, it is presumed that, regarding solder paste, solder is in powder form with an extremely large surface area, so oxidation of Sn—Zn-based solder becomes severe in the preheating stage, resulting in a significant adverse effect on solderability.

Oxidation of Sn-Zn based lead-free solder powders during the preheating phase can be prevented if oxygen is almost completely removed from the atmosphere inside the furnace, as realized in _N2 reflow furnaces. However, _N2 reflow furnaces are expensive and have high operating costs.

It has been found that, according to the present invention, by adding at least one isocyanuric acid compound to the rosin-based flux used to mix the solder powder to prepare the solder paste, the lead-free solder powder based on Sn-Zn can be prevented from being damaged during the preheating process. The oxidation of the isocyanuric acid compound is selected from isocyanuric acid without hydroxyl and its derivatives. While not wishing to be bound by a particular theory, the reason for this is assumed to be as follows.

Isocyanuric acid compounds generally have high heat resistance, and they do not decompose during heating at 150-170° C., which is a standard preheating condition in a remelting furnace, for 30-100 seconds. Therefore, if a flux containing an isocyanuric acid compound is used to prepare a Sn-Zn based solder paste, during the preheating process in a reflow furnace, the isocyanuric acid compound will cover the surface of the Sn-Zn based solder powder, which may Effectively prevent its surface from oxidation.

One reason for using an isocyanuric acid compound not having a hydroxyl group is as follows. To improve wetting, rosin-based fluxes used to prepare solder pastes contain an activator. The activator typically comprises a hydrohalide salt of an organic amine. In the presence of polar species, amine hydrohalides can react with Sn-Zn based solder powders prior to soldering, especially when printing is performed when the solder paste is exposed to air. Due to this reaction, the viscosity of the solder paste changes, and generally increases, making smooth printing difficult. This trend is particularly strong with Sn-Zn-based lead-free solder pastes, so the use of polar substances can be avoided. Since isocyanuric acid derivatives having a hydroxyl group show polarity, they are not used in the flux used for the solder paste according to the present invention.

If an isocyanuric acid derivative having a hydroxyl group is used in a flux for a Sn-Zn-based lead-free solder paste, the zinc on the powder surface may be oxidized so that the surface becomes white during washing with water, which in After welding. This is another reason why isocyanuric acid derivatives having hydroxyl groups are not suitable for Sn-Zn based lead-free solder pastes.

Examples of isocyanuric acid compounds suitable for use in the present invention are isocyanuric acid and its derivatives having the formula:

wherein R ₁ -R ₃ , which may be the same or different from each other, represent hydrogen, alkyl optionally substituted by halogen, or allyl. The alkyl group is preferably a lower alkyl group having 1 to 6, preferably 1 to 4 carbon atoms. The compound wherein R ₁ -R ₃ are all hydrogen is isocyanuric acid. The compound in which they are both alkyl groups is a trialkyl isocyanurate.

Specific examples of such isocyanuric acid compounds include isocyanuric acid, trimethyl isocyanurate, triethyl isocyanurate, tripropyl isocyanurate, butyl isocyanurate, tris(2 , 3-dibromopropyl) isocyanate, triallyl isocyanurate, etc. One or more isocyanuric acid compounds may be used.

Preferred isocyanuric compounds for use in the present invention are isocyanuric acid and tris(haloalkyl)isocyanurates (compounds of the above formula wherein R ₁ -R ₃ are haloalkyl) such as tris(2,3-di bromopropyl) isocyanurate. They can be used simultaneously. In particular, isocyanuric acid is preferably used alone or as a mixture with another isocyanuric acid compound.

The amount of isocyanuric acid compound present in the rosin-based flux is 0.5-10.0% by weight. If the amount is less than 0.5% by weight, the effect of preventing surface oxidation of Sn—Zn-based solder powder during preheating cannot be sufficiently achieved, while if it exceeds 10% by weight, solderability is reduced. The amount of the isocyanuric acid compound added to the flux is preferably 2 to 6% by weight.

According to another aspect of the present invention, a solder paste comprises Sn-based lead-free solder powder and a rosin-based flux comprising 0.01-10.0% by weight of at least one compound selected from salicylamide (=salicylic acid amide ) and its derivatives of salicylamide compounds.

While not wishing to be bound by a particular theory, it is hypothesized that the salicylamide compound is preferentially adsorbed by the surface of the solder powder, and thus, it prevents the solder powder from reacting with flux components, especially with activators such as amine hydrohalides. Reacts with organic acids. As a result, the change (mainly increase) of the viscosity of the solder powder caused by this reaction is prevented, and the solder paste can be smoothly fed by printing or dispensing even after long-term storage. Salicylamide compounds have been found not to interfere with the reflow properties of solder pastes.

The effect of the salicylamide compound in suppressing the viscosity change of the solder paste was observed with a solder paste containing powder of any Sn-based lead-free solder, including Sn-Ag-based and Sn-Zn-based solders .

The salicylamide compound used in the present invention includes salicylamide, decanedicarboxylic acid disalicylhydrazide, 3-(N-salicyloyl)-amino-1,2,4-triazole and the like. If the amount of the salicylamide compound present in the rosin-based flux is less than 0.01% by weight, the above-mentioned effects cannot be appreciably achieved. If it is more than 10.0% by weight, melting of solder powder may be suppressed, resulting in formation of solder balls during soldering. The amount of salicylamide in the flux is preferably from 0.1 to 3.0% by weight.

As elucidated before, the salicylamide compound seems to exert its ability to suppress the viscosity change of the Sn-based lead-free solder paste by adsorbing to the surface of the Sn-based lead-free solder powder in the solder paste. Therefore, instead of adding the salicylamide compound to the flux, it is also possible to pre-adsorb the salicylamide compound to the surface of the solder powder by surface treatment of the solder powder by, for example, dissolving it in a suitable volatile solvent. A solution of salicylamide compound in the solder is sprayed onto the surface of the solder powder or the solder powder is immersed in the solution, and then the solvent is evaporated. The thus obtained Sn-based solder powder having the salicylamide compound deposited on its surface by adsorption may be mixed with a rosin-based flux not containing the salicylamide compound to prepare a solder paste.

Therefore, the present invention also provides a method for preparing a solder paste, which comprises surface-treating a Sn-based lead-free solder powder solution of a salicylamide compound in an organic solvent, and depositing the obtained salicylamide on the surface thereof. The compounded solder powder is mixed with a rosin-based flux.

In this method, the surface treatment is preferably performed such that the amount of the salicylamide compound deposited on the solder powder is 0.01 to 10.0% by weight based on the flux mixed with the surface-treated solder powder in the next step. weight.

The flux used in the solder paste according to the present invention is a rosin-based flux having rosin as a main component. Typically, rosin-based fluxes contain rosin, activators, thixotropes and solvents. Except for adding an isocyanuric acid compound or a salicylamide compound to the flux according to the present invention, types and amounts of other components of the flux may be the same as conventional rosin-based fluxes without particular limitation. For the solder paste according to the present invention, the fluxing agent may also contain an isocyanuric acid compound and a salicylamide compound, each in an amount within the above-mentioned range, so as to further improve the solderability of the solder paste.

The rosin can be a natural, unmodified rosin, such as gum rosin, tall oil rosin, or wood rosin, or it can be a modified rosin such as polymerized rosin, hydrogenated rosin, rosin ester, or rosin modified resin. Of course, two or more of them may be used.

As activators, preference is given to using hydrohalides, especially hydrobromides of organic amines. The organic amine can be primary (eg ethylamine), secondary (eg diethylamine) or tertiary (eg triethylamine). Heterocyclic amines such as pyridine, aromatic amines such as aniline, alicyclic amines such as cyclohexylamine, compounds having two or more amino groups such as diphenylguanidine can also be used.

Preferably in addition to the amine hydrohalide activator, an organic acid activator such as stearic acid and sebacic acid or another activator may also be used.

Hardened castor oil, amides or similar are commonly used as thixotropic agents.

Examples of solvents are carbitols such as butyl carbitol and hexyl carbitol, and alcohols such as terpineol and halogenated alcohols.

The amount of the above-mentioned components in the flux is calculated by weight percentage, for example, 35-60% of rosin, 0.5-10% of activator, and 1-10% of thixotropic agent. The amount of amine hydrohalide activator is preferably 0.5-5%. Of course, according to the present invention, the fluxing agent also contains isocyanuric acid compound and/or salicylamide compound. In addition to those mentioned above, the flux may contain one or more additives.

According to the present invention, the Sn-based lead-free solder powder used in the solder paste may be an alloy powder mainly containing Sn and including one or more elements of Ag, Cu, In, Sb and Zn. Preferably, the Sn-based lead-free solder is a Sn-Ag alloy (such as Sn-3.5Ag), a Sn-Ag-Cu alloy (such as Sn-3Ag-0.5Cu), a Sn-Zn alloy (such as Sn-9Zn), or Sn-Zn-Bi alloy (such as Sn-8Zn-3Bi), wherein the number before the element indicates the content of the element in weight percentage. To further lower the melting point, increase mechanical strength or inhibit solder oxidation, these Sn-based lead-free solders may also include one or more of Bi, In, Ag, Ni, Co, Mo, Fe, P, Ge, Ga or the like.

In an embodiment of the present invention, wherein the flux contains an isocyanuric acid compound, the Sn-based lead-free solder is preferably a Sn-Zn-based solder such as a Sn-Zn alloy or a Sn-Zn-Bi alloy. As mentioned earlier, the presence of isocyanuric acid compounds in the flux is very effective in preventing the oxidation of solder powder during the preheating stage in the reflow furnace. Therefore, when this embodiment is carried out on a solder paste containing Sn—Zn-based lead-free solder powder which is highly sensitive to oxidation, a particularly remarkable effect can be obtained.

On the other hand, the second embodiment of the present invention can be satisfactorily practiced on a solder paste comprising any Sn-based lead-free solder powder, wherein the fluxing agent comprises a salicylamide compound, said Sn-based lead-free solder comprising Sn-Ag-based alloys and Sn-Zn-based alloys, although the effect on Sn-Zn solder is stronger than that on Sn-Ag solder.

The shape of the solder powder is not limited, but generally it is a spherical powder, which can be prepared by a centrifugal atomization method, a gas atomization method, or the like. The particle size of the solder powder can be the same as that of conventional solder paste, typically around 200-400 mesh, although 500 mesh or finer powders can also be used.

The mixing ratio of solder powder and flux can be selected to obtain a solder paste with a viscosity suitable for printing or dispersing. Typically, flux is 5-20% by weight, with the remainder being solder powder.

The following examples are described to further explain the invention. These examples are generally illustrative rather than restrictive. In the examples, percentages represent percentages by weight if not indicated.

Example

(Examples 1-3 and Comparative Example 1)

88.5% spherical powder of Sn-Zn-based lead-free solder alloy having the following composition: 8% Zn , 3% Bi and the rest being Sn, the rosin-based flux had the composition shown in Table 1.

Using the solder paste prepared above, a reflow test was performed in a two-stage heating type standard reflow furnace in which preheating and main heating were performed under normal conditions, and solderability (wettability) and solder balls were evaluated. form. The results are shown in Table 1.

Table 1 Flux composition (weight%) Example 1 Example 2 Example 3 Comparative example 1 polymerized rosin 44 41 41 46 Diphenylguanidine HBr 2 2 2 2 hardened castor oil 5 5 5 5 Isocyanuric acid 2 - 1 - Tris(2,3-dibromopropyl)isocyanurate - 5 4 - 2,3-Dibromo-1-propanol 2 2 2 2 alpha-terpineol 45 45 45 45 test results Example 1 Example 2 Example 3 Comparative example 1 solder ball none a small amount none a lot of Brazing outstanding good outstanding Difference

From the results in Table 1, it can be seen that when reflow soldering is performed in air under standard conditions with a solder paste based on Sn-Zn solder (the solder paste uses an isocyanuric acid compound-containing auxiliary according to the present invention flux), it was significantly superior to the solder paste of Comparative Example 1 in terms of solder ball formation amount and solderability, in which no isocyanuric acid compound was added to the flux.

(embodiment 4-5 and comparative example 2-3)

88.5% spherical powder of Sn-Zn-based lead-free solder alloy or spherical powder of Sn-Ag-based lead-free solder was thoroughly mixed with 11.5% rosin-based flux to prepare solder paste. The lead-free solder alloy has the following composition: 8% Zn, 3% Bi and the rest is Sn, the Sn-Ag based lead-free solder has the following composition: 3% Ag, 0.5% Cu and the rest is Sn, the rosin-based flux has the composition shown in Table 2.

The solder pastes prepared above were left at room temperature to determine shelf life, which is the period of solder paste's ability to maintain a printed or dispensed paste as an index for evaluating the rate of change in viscosity of the solder paste. The results and the type of solder powder are shown in Table 2.

Table 2 Flux composition (weight%) Example 4 Example 5 Comparative example 2 Comparative example 3 polymerized rosin 49 47 50 49 Diphenylguanidine HBr 1 1 1 1 stearic acid 5 5 5 5 hardened castor oil 5 5 5 5 Decanedicarboxylic acid disalicyyl hydrazide 1 - - - 3-(N-salicyloyl)-amino-1,2,4-triazole - 2 - - 2,3-Dibromo-1-propanol - 2 - 2 alpha-terpineol 38 38 38 38 Solder Powder/Test Results Example 4 Example 5 Comparative example 2 Comparative example 3 Solder powder Sn-8Zn-3Bi Sn-3Ag-0.5Cu Sn-8Zn-3Bi Sn-3Ag-0.5Cu Storage life >12 weeks >12 weeks 1 week 6 weeks

As can be seen from Table 2, the conventional lead-free solder pastes of Comparative Examples 2 and 3, in which the flux did not contain salicylamide, lost their paste and were not suitable for use in Sn-Ag based solders after 6 weeks, even after 1 It is also not suitable for more reactive Sn-Zn based solders. In contrast, in accordance with the present invention, adding a salicylamide compound to the flux increases the shelf life of the solder paste by at least about 2 times for Sn-Ag based solders and at least about 6 times for Sn-Zn based solders, stating It can effectively suppress the viscosity change of Sn-based lead-free solder paste.

Industrial applicability

The present invention provides a Sn-based lead-free solder paste that has improved solderability and can be satisfactorily used in conventional reflow soldering methods. As a result, in certain cases, such as solder pastes containing Sn-Zn-based lead-free solder powders that are highly sensitive to oxidation, the use of an activator containing an appropriate amount as usual can provide a solder paste in which the formation of solder balls is inhibited, and it has excellent wetting properties. It is also possible to suppress the viscosity change of the Sn-based lead-free solder paste containing the Sn-based solder powder, including the Sn-Ag-based solder and the Sn-Zn-based solder, thereby making it possible to remarkably prolong the use of this solder. A lead-free solder paste that is easy to print or dispense.

Although the invention has been specifically described with respect to the preferred embodiments, these embodiments are only illustrative and do not limit the invention. It will be appreciated by those skilled in the art that various modifications may be made to the above-described embodiments without departing from the scope of the present invention as set forth in the claims.

Claims (10)

1. one kind comprises the solder(ing) paste based on the lead-free solder powder of Sn that mixes mutually with flux based on rosin, it is characterized in that described flux based on rosin comprises at least a salicylamide compound of 0.01-10.0 weight %, described salicylamide compound is selected from salicylamide and its derivative.

2. according to the solder(ing) paste of claim 1, wherein said lead-free solder is selected from the scolder and the scolder based on Sn that contains Zn based on Sn that contains Ag.

3. according to the solder(ing) paste of claim 1, wherein said salicylamide compound is selected from salicylamide, the last of the ten Heavenly stems dicarboxylic acids two salicylyl hydrazines and 3-(N-salicyloyl)-amino-1,2,4-triazole.

4. according to the solder(ing) paste of claim 2, the scolder based on Sn of the wherein said Ag of containing also comprises Cu.

5. according to the solder(ing) paste of claim 2, the scolder based on Sn of the wherein said Zn of containing also comprises Bi.

6. according to the solder(ing) paste of claim 1, wherein said flux based on rosin comprises activator.

7. according to the solder(ing) paste of claim 6, wherein said activator comprises at least a organic amine hydrohalide.

8. according to the solder(ing) paste of claim 1, it is characterized in that described flux based on rosin also comprises at least a isocyanuric acid compound of 0.5-10.0 weight %, described isocyanuric acid compound is selected from isocyanuric acid with hydroxyl and its derivative.

9. according to the solder(ing) paste of claim 8, wherein said lead-free solder is the scolder based on Sn that contains Zn.

10. according to the solder(ing) paste of claim 8, wherein said isocyanuric acid compound is selected from isocyanuric acid and isocyanuric acid three-haloalkyl ester.